This invention relates generally to the field of chemical synthesis, and more particularly to methods and compositions for the preparation of multifunctional carbonates, curing agents prepared from them, and epoxy formulations prepared with the curing agents.
Multifunctional carbonates are useful chemical compounds that can be used directly, or as intermediates in the preparation of other materials. They can be used to prepare polyurethanes, polyurethane polyureas, polyamide polyurethane polyols, polyether polyurethane polyols, polycarbonate polyurethane polyols, and curing agents for epoxy resins.
Multifunctional carbonate compounds have traditionally been formed using polyglycidyl ethers as starting materials. While this is an effective method of producing the desired compounds, the polyglycidyl ethers are relatively expensive materials, which can make some applications of the resulting products economically disadvantageous.
There is a need for a method of producing multifunctional carbonates, for such downstream uses as forming polyurethanes and epoxy curing agents, which makes use of relatively inexpensive and readily available starting materials.
The present invention provides a more economical method of producing multifunctional carbonate resins. It overcomes the disadvantage of using relatively expensive starting materials, such as polyglycidyl ethers, that have traditionally been used.
One form of the present invention is a method for preparing a carbonate urethane compound by reacting a carbonate containing compound that also contains a reactive hydroxyl group with a compound containing at least two isocyanate groups. The reaction is performed in a solvent and in the presence of a base.
Another form of the present invention is a composition for a curing agent that is a compound containing two or more first carbamate linkages, where each first carbamate linkage is connected to a second carbamate linkage. The ester side of the first carbamate linkages are connected to the ester side of corresponding second carbamate linkages. In addition, there is a terminal amine group connected to the amido side of the second carbamate linkages.
Although this description discloses the making and using of various embodiments of the present invention, these specific embodiments are merely illustrative of a specific way to make or use the present invention, and are in no way meant to limit it. The present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts.
The present invention makes use of readily available and inexpensive multi-isocyanate compounds reacted with organic carbonates that contain pendant hydroxyl groups to produce products that contain two or more carbonate functionalities. These compounds, that contain two or more carbonate groups, are defined for the purposes of this application as xe2x80x9cmultifunctional carbonates.xe2x80x9d The preparation of the multifunctional carbonates of the present invention is done without the need for the formulator to directly handle an isocyanate compound in order to make a curing agent.
The multifunctional carbonates of the present invention can be further modified by reaction with diamines to produce compounds containing a multiplicity of carbamate linkages, and having terminal amine groups.
The present invention is capable of producing compounds that provide advantages in the curing of epoxy resins. Derivatives produced by the methods of the present invention react more quickly with epoxy resins than examples prepared by methods in the prior art. In addition, the cured epoxies produced have superior toughness and adhesion properties over those produced by previously disclosed methods.
One form of the present invention is a method for preparing a carbonate urethane compound by reacting a carbonate containing compound that also contains a reactive hydroxyl group with a compound containing at least two isocyanate groups. The reaction is performed in a solvent and in the presence of a base.
Another form of the present invention is a composition for a curing agent that is a compound containing two or more first carbamate linkages, where each first carbamate linkage is connected to a second carbamate linkage. The ester side of the first carbamate linkages are connected to the ester side of corresponding second carbamate linkages. In addition, there is a terminal amine group connected to the amido side of the second carbamate linkages.
Yet another form of the present invention is a method for preparing a curing agent by reacting a compound containing at least two carbamate linkages, where each carbamate linkage is connected to at least one carbonate, with an excess of a diamine. The reaction is performed in a solvent. A carbamate linkage, as referred to in this application, with the ester and amido sides labeled is shown below. 
Another form of the present invention is a method of curing an epoxy resin by reacting the resin with a curing agent having one of the general structures: 
where R1 is an alkyl or aryl unit, R2 is a spacer chain of two to two hundred atoms in length, R3 is independently hydrogen or an alkyl, aryl or polyether segment, and n=2 or 3. The term xe2x80x9cspacer unitxe2x80x9d refers to a chain of atoms that may be straight or branched. The length of the spacer chain is defined in terms of the number of atoms in the backbone of the spacer chain that connects the two units in question. A nonlimiting example of a six atom spacer chain would be a hexamethylene chain, as shown below. 
Yet another form of the present invention is the reaction product of an epoxy resin and a curing agent, where the curing agent is a compound containing two or more first carbamate linkages, where each first carbamate linkage is connected to a second carbamate linkage. The ester side of the first carbamate linkages are connected to the ester side of corresponding second carbamate linkages. In addition, there is a terminal amine group connected to the amido side of the second carbamate linkages.
The isocyanate containing compounds used in the present invention can be essentially any alkyl, aryl or mixed alkyl and aryl compound that contains two or more isocyanate groups. These compounds include, but are not limited to, 1,3 phenylene diisocyanate; 1,4 phenylene diisocyanate, 1,4 diisocyantobutane; 1,6 diisocyanatohexane, 1,8-diisocyanatooctane; 2,4,6 trimethyl-1,3phenylene diisocyanate; 3,3xe2x80x2-4,4xe2x80x2biphenylene diisocyanate; trans-1,4-cyclohexylene diisocyanate; xcex1-4-tolylene diisocyanate; isophorone diisocyanate; m-xylylene diisocyanate; methylene di-p-phenyl diisocyanate; toluene 2,4 disocyanate; toluene 2,6 diisocyanate.
The diamines used in some of the embodiments of the present invention can be essentially any alkyl, aryl or mixed alkyl and aryl diamine. Examples include, but are not limited to; 1,3 diaminopropane; 1,4 diaminobutane; 1,6 diaminohexane; 1,2 diaminobenzene; 1,3 diaminobenzene; 1,4 diaminobenzene; 2,3 diaminotoluene; 2,4 diaminotoluene; diaminoxylene; ethylenediamine; diethylene triamine, triethylenetetramine.
Essentially any commercially available epoxy resin may be used in the embodiments of the present invention that require one. Non-limiting examples of epoxy resins that are appropriate for use in the present invention include EPON 828(copyright) (Shell/Resolution Polymers), Epotuf 37-140(copyright) (Reichhold), DER 331(copyright) (Dow), GY-6010(copyright) (Vantico).
For the embodiments of the present invention that employ a solvent, the solvent may be a pure solvent or a mixture. Any solvent that at least partially dissolves the reactants and does not react with the reactants may be used. The choice of an appropriate solvent will be apparent to one of ordinary skill in the art.